1. Field of the Invention
The present invention relates to a flow amount control valve, which is capable of controlling a flow amount of a pressure fluid that flows through and between a pair of ports, by axial displacement of a rod possessing a valve element.
2. Description of the Related Art
Heretofore, a flow amount control valve has been known, in which an inner cylinder, having a threaded part on an inner circumferential surface thereof, is disposed rotatably inside of a valve housing. At the interior of the inner cylinder, a valve body is fixed at one end thereof, and a valve shaft having a threaded part on an outer circumferential surface thereof is inserted, wherein the inner cylinder and the valve shaft are screw engaged mutually with each other.
In such a flow amount control valve disclosed in Japanese Laid-Open Patent Publication No. 2006-057663, as shown in FIG. 9 of the present application, a piston 1 is provided, which is displaceable under the supply of a pressure fluid, and a control side bellows valve body 3 is engaged on a lower end of a sliding shaft 2 that is connected to the piston 1. Further, a compensation side bellows valve body 5 is connected to a lower portion of the control side bellows valve body 3 through a connecting rod 4. The control side bellows valve body 3 includes a flexible bellows portion 3c, which is connected to a fixed mounting member 3a and a columnar member 3b, whereas the compensation side bellows valve body 5 includes a flexible bellows portion 5c, which is connected to a fixed mounting member 5a and a columnar member 5b. In addition, while the bellows portions 3c, 5c are caused to expand and contract through displacement of the piston 1, the control side bellows valve body 3 and the compensation side bellows valve body 5 are displaced.
With the aforementioned conventional technique, the control side bellows valve body 3 and the compensation side bellows valve body 5 are mutually connected through the connecting rod 4. One end of the connecting rod 4 abuts against and is supported by a hemispherical surface on a recess of the columnar member 3b making up the control side bellows valve body 3, and the other end thereof is inserted through and supported within a recess of the columnar member 5b making up the compensation side bellows valve body 5.
However, because the control side bellows valve body 3 and the compensation side bellows valve body 5 are not each respectively connected completely with respect to the connecting rod 4, there is a concern that the control side bellows valve body 3, the connecting rod 4 and the compensation side bellows valve body 5 tend to deviate or shift perpendicularly and become off-centered. Stated otherwise, because the control side bellows valve body 3 and the connecting rod 4 are merely in abutment with each other by means of the semispherical surface that simply abuts in the recess, and displacement in the direction perpendicular to the axis thereof is not regulated in any way, it is problematic and difficult for the control side bellows valve body 3 and the connecting rod 4 to remain arranged on the same axis.
Owing thereto, the control side bellows valve body 3 and the compensation side bellows valve body 5 tend to shift relatively through the flexible bellows portions 3c, 5c out of alignment in the perpendicular direction with respect to the axis, and it is difficult for the control side bellows valve body 3 and the compensation side bellows valve body 5 to be displaced in a straight line along the axial direction. As a result, accuracy of the flow amount control performed by the control side bellows valve body 3 and the compensation side bellows valve body 5 tends to be deteriorated.